An assessment of the age and tectonic setting of volcanics near the base of the Windermere supergroup in northeastern Washington: implications for latest Proterozoic-earliest Cambrian continental separation.

New geochemical and isotopic data are presented for the mafic metavolcanics of the Huckleberry formation analysed by K/Ar techniques in an attempt to assess their tectonic setting and age of extrusion. Major- and trace-element compositions are found to be consistent with the rift setting previously interpreted for the Windermere supergroup. Isotopic analyses, although inconclusive with respect to the true age of the Huckleberry volcanics, indicate that the Rb-Sr system has been disturbed subsequent to extrusion of the volcanics, and therefore the K/Ar ages should be considered suspect. Recent isotopic data from the N Canadian Cordillera tend to indicate that the Windermere supergroup may in fact be younger, in closer agreement with the ages for breakup indicated by the subsidence analyses.-J.M.H.